WieWaldi The big downside are the mini-keys with 20 mm of width (white keys are 20 mm, whereas white keys on a full size keyboard are almost 24mm wide). This means if you practice there something with an octave, your muscle memory would hit a seventh when you are back on your main piano.
I wish acoustic and digital pianos come in multiple sizes that can fit small-handed people like me without compromising sound quality and features. At standard size, an octave spans 6.5 inches (165mm, or 23.6mm per key). I read that Hailun makes narrower ones at 6.0 inches (21.8mm per key), and 5.5 inches (20.0mm per key).
There is also a fascinating video of one guy in Pennsylvania that retrofits grand piano with narrower keys.